At the present time, devices for hydraulic conveyance of loose materials, comprising a chamber provided with a loose material charging unit and a slurry discharge unit and making integral part of hydraulic conveyance installations incorporating additional components such as water pumps, pipelines, stop valves and fittings, should meet a number of requirements including reliable operation of such devices ruling out clogging of the discharge unit with the loose material, or hanging of the loose material in the chamber, which stems from the strength of the chamber; as well as efficient charging of the loose material resulting from minimized amounts of the loose material particles carried away with the liquid being discharged during filling and minimized amount of air fed into the chamber. Another requirement to be met resides in efficient slurry discharge due to low classifying of the loose material which is uniformly fed to the discharge unit.
One state-of-the-art device for hydraulic conveyance of loose materials is known (SU, A, No. 615,015) to comprise a vertically installed chamber having a cylindrical shape and provided with a pipe for charging the loose material in the form of slurry, which pipe also serves as a pipe for discharging the slurry into a pulp feeding pipe, a pressure liquid flow feeding pipe, and a liquid discharge pipe located in the top portion of the chamber.
To minimize the amount of the loose material particles carried away with the liquid being discharged, the chamber is charged in an upward flow, while the liquid being discharged is separated from the loose material being charged, by means of a screen which is adapted to move lengthwise the chamber as it is being charged from below and intended to reduce the amount of the loose material particles carried away by the liquid being discharged.
Provision of a movable screen inside the chamber renders the construction more sophisticated and reduces its reliability. Moreover, charging the slurry in an upward flow results in intense classifying of the loose material in terms of density and size, which is also the case during discharge of the chamber, with attendant instability of the slurry density.
Thus, the aforedescribed device fails to provide the conveyance of stable density slurry to the pulp feeding pipe, while a reduction in the amount of the loose material carried away by the liquid being discharged is attained at the expense of reliability of the device.
One more prior-art device for hydraulic conveyance of loose materials (SU, A, No. 391,974) is known to comprise a vertically installed chamber having a cylindrical shape. Preparatory to charging, part of the liquid is expelled from the chamber through a pipe provided in its bottom portion, in order to minimize the amount of the loose material carried away.
To reduce the classifying taking place, when the chamber is being discharged, the pressure liquid flow is divided into two flows fed into the chamber through two pipes one of which is located in the top portion of the chamber.
The additional operations such as draining the liquid preparatory to charging and delivery of the part of the liquid flow during discharge, considerably reduce the efficiency of the device and render its control system more sophisticated. At least three chambers are required to enable continuous discharge of the slurry into the pulp feeding pipe. The aforementioned device features low reliability resulting from the fact that the chamber may only be charged with dry or dehydrated material tending to hang up in the chamber, which promotes clogging of the discharge pipe if water content of the loose material is too low.
By-passing part of the pressure liquid flow upward the chamber reduces the stability of slurry density, because in the course of discharging the ratio between the pressure liquid flow rates is changed due to increased rate of the pressure liquid make-up flow. Effective control over the ratio between the rates of the main flow and the make-up (upper) flow of the pressure liquid is virtually unfeasible.
Known presently are other devices for hydraulic conveyance of loose materials (SU, A, No. 612,873; SU, A, No. 798,000) where attempts have been made to reduce the amount of the loose material particles carried away during charging.
In the former of the embodiments mentioned hereinbefore, air is force fed into the top portion of a cylindrically shaped chamber during discharge. As a result, after discharge is over, the chamber remains empty without the need to drain the liquid.
However, the above-described device offers but a low margin of safety because of possible loss of leak-tightness of the chamber, with attendant hazard of compressed air bursting. Power consumption of the device is far too high to effect hydraulic conveyance over long distances. This predetermines the use of a compressor having a power capacity greater than that of the primary pressure unit--the water pump. Furthermore, the device suffers from low production efficiency resulting from the fact that the device can only be charged when the pressure inside the chamber is reduced to the atmospheric pressure.
In the latter of the devices mentioned hereinbefore, the chamber is made in the form of a hydraulic cyclone, which allows the discharged liquid to be separated and diverted while the slurry is being charged into the chamber. In such an embodiment, the top portion of the chamber operating as a hydraulic cyclone, is subject to fast wear, which in turn affects adversely the chamber strength characteristics.
In the above-discussed devices, the chamber discharge process is accompanied by classifying of the loose material taking place as it is being expelled from the chamber by the liquid. The classifying occurs due to segregation of the loose material as it descends, the smaller and lighter particles being suspended.
Still another device for hydraulic conveyance of loose materials (U.S. Pat. No. 1,168,496) is known to comprise a toroidal chamber having a meridianal plane and an equatorial plane and provided with pipes for charging the loose material and discharging the liquid used for hydraulic conveyance, both of the pipes being arranged on one side with respect to the meridianal plane of the toroidal chamber, and with a slurry discharge device arranged on the other side with respect to the meridianal plane, the equatorial plane of the chamber being disposed vertically.
The toroidal shape of the chamber contributes to its higher strength and minimizes specific metal consumption.
Loose materials can be charged into the toroidal chamber in the form of slurry by loading it in a standstill zone on the surface of the throat of the toroidal chamber, that is on the inner wall in its upper portion. From the inner wall, the loose material slips down until lumps of the material drop down in a restrained manner, thus minimizing the amount of the loose material particles carried away by the liquid discharged because additional energy is required to break the particles loose from the bulk of the material. Besides, the portion of the toroidal chamber disposed above its throat used for charging the loose material, has a larger cross-section than the aforedescribed chambers having different shapes but the same volume. Because of this, the uplift rate of the liquid being discharged is less than that in any of the above-mentioned devices, and it tends to decline still further as the distance between the cylindrical portions of the chamber or the chamber throat radius increases.
However, as the operating efficiency of such devices increases, which involves greater flow rates of the slurry being handled, the amount of the loose material particles carried away by the liquid discharged tends to increase as well, since the material charging portion of the throat fails to accept all the loose material fed in, with the result that part of the loose material is repelled by the throat surface, thus causing slurry swirling flows.
As compared to chambers of the other shapes described hereinbefore, use of a toroidal chamber enables the loose material to be more uniformly fed to the discharging unit, and the loose material is less liable to classifying by virtue of the fact that the loose material is circumfluent the lower portion of the throat surface in a downward flow, whereas the liquid is circumfluent the same throat portion in an upward flow. Such an arrangement of the flows makes it possible to reduce the resistance of the liquid to the loose material because of the fact that the major liquid flow is formed nearby the throat wall, viz., close to the inner wall of the chamber. However, in common with the aforedescribed devices, as the height of the vertical cylindrical portions of the chamber increases, the loose material is liable to be segregated by particle size and density, as for height of these portions, which is causative of classification and reduced stability of the slurry density.